9Gb to 4.7Gb without re-encoding video how often?

[markrb]

I am starting to look into DVD-R converts and one thing keeps bugging me when I read the guides and the forum. Everyone seems to always re-encode the video to get it a bit smaller.
Considering the number of extra's on some of the discs out there there must be a good deal of discs you just don't need to make smaller if you remove all the extra's.
Is this true?
If so what is the percentage?
Do you always have to re-encode the video?

Thanks,
Mark

[jdobbs]

You'll see many movies (typically older ones) that are authored as single layer -- those will come over as-is.

Rarely (very rarely) you will see a disc that is barely over the 4.7GB limit and removing some extra languages or a couple of extras will get you down small enough.

But... most of time, you will see that the DVD's authors used most of the 9GB available to them -- and you will need to reencode. Their reasoning is solid, if they have to go to the time and expense of creating a dual layer DVD, it makes complete sense to use as much of it as you can and increase the quality...

[Kenwood]

Just one thing is bugging me.
If you can get your hands on the movie: The Fugitive you will see that is almost 128 mins. long.
When you decrypt the DVD (at least the PAL euro version I have) you will see that the whole movie won't take up than 3.8 GB.
It's a DVD-5.
De movie is full Widescreen (16:9 Anamorhic) so with no black fillings above ore below the main movie screen.
So, it's possible to put a movie that is more than 2 hrs on a single layer DVD.
Did last night a re-encode of: We Were Soldiers.
Total movie time: 133 mins.
After remux, burn etc put the DVD in my settop player en guess what ?
Great video quality throughout the movie !
So it's possible.
The way I see it, is to compare it with making a MP3.
You can do that at 128/160/192 or 320 kilobits per second.
But you will have to ask youself: What samplerate is enough, that keep good quality for me ?
I personal don't go higher than 160 kilobits per second, that good enough for me.
But, I think the movie studio's over-sample the commercial DVD to make it as difficult as it can.
They don't like it when you make a back-up they only want to sell for big bucks a DVD to you.
Where I live a recent DVD can cost up to 35-40 Euro, compare that to other countries or look on the Internet.
They also use a strange first GOP key, so that after a re-encode with ReMpeg2 1.5.2. at some points many movies start to shake for a while.
Now using TMPGEnc en this one does the trick very good, but you will have modify many options yourself and this program is not affected by the strange key.
At this moment I'trancoding Black Hawk Down (139 mins.) can wait to see the outcome.
After that -> The Abyss (Director Cut - 163), but will put this one on a RW first.
Can't wait !
Best regards,

Kenwood

[jdobbs]

How much can fit on a DVD-R depends on a lot of variables. But mainly it's the complexity of the film. High action, high contrast films require more bandwidth than low light, low action.

Another factor is the quality of the encoder. If you use a low quality encoder, like ReMPEG2, you need more bandwidth to get a decent picture. Also, with the use of variable bitrate as opposed to constant bitrate, you can use the available bits more efficiently.

Finally is where you set the bar. There is no such thing as a perfectly encoded MPEG-2 stream because it uses "lossy" compression. To get perfection you'd need a compression algorithm that returns an exact digital match to the picture fed in. Run length, LZW, and Huffman encoding can all provide that --> but they aren't very efficient with video because of it's nature.

So you have to decide how good is "good enough". One of the great things about CCE is the "Advanced" feature in which you can see the level of distortion calculated and can choose a point on the "Q" scale that your experience tells you meets your definition of "good enough". The Robshot method recommends below "9" -- but some folks like it lower. A good author knows that to make the best DVD you use all the bits available to you, so you raise the bitrate until you fill the disc.

But if your goal is to get a lot on a DVD-R you can raise the "acceptable" level until it is too much for your personal tastes. I've gotten as much as 4 hours on a DVD-R with great results (a good example is Lawrence of Arabia -- which has a lot of low motion art shots).

BTW -- I like to go 192Kbs on my MP3s -- I have to have that close-to-cd perfection.